It has long been known that ozone is a very powerful oxidizer, and ozone is employed in a variety of processes for a variety of purposes. One of the most significant of those purposes is treatment of water, both in processes for production of potable water and in processes for the treatment of waste water. Ozone is effective as a water treatment agent for the reduction of BOD and COD, VOC's, and bacterial and viral pathogens, and is also beneficial in the removal of small particles and metal compounds. For a variety of reasons, including the fact that ozone can be efficiently generated at the treatment site, requiring only electricity and dry air, it is rapidly becoming the preferred water treatment agent for use at remote sites and/or in undeveloped regions. Ozone is also increasingly being used in established treatment facilities as a replacement for chlorine.
The majority of the ozone used in water treatment facilities is generated in what are referred to as corona discharge generators, in which dry oxygen is passed through a corona discharge field created by imposing a high voltage electrical potential on a conductive electrode that is disposed in proximity to a dielectric material imposed between the electrode and an electrical ground. Most commonly, dried air is the feedstock to the generator and ozone is created from the oxygen component of the air. Dried gas mixtures containing higher concentrations of oxygen, up to and including pure oxygen, may certainly be used, but the additional cost and complexity of that approach is usually not justified by the higher ozone output that can be achieved. For purposes of this application, the feedstock gas is referred to as air, and it is to be understood that other oxygen containing gas mixtures, or pure oxygen, could be used within the scope of the described invention. The high electrical potential difference allows a corona discharge field to form between the electrode and dielectric. As air is passed through that field, some of the molecular diatomic oxygen (O2) is ionized, and some of the ions recombine in triplets as ozone (O3). Most high capacity ozone generators are of the Kerag type, in which ozone is generated in a plurality of ozone generating cells that are contained within a generator enclosure. Each ozone generating cell comprises, typically, an elongate electrode that is suspended within the interior of, but not in contact with, an elongate hollow dielectric tube, typically of glass or ceramic. In ozone generators of the prior art, the dielectric tubes are supported at their upper, open ends, by a support plate or seal plate, with each dielectric tube extending through an aperture in the plate downward into a container of water. The water is used for cooling as well as being a grounded electrical conductor. In the prior art generators, each electrode is supported at its upper end by an electrode support plate which, like the dielectric tube support plate, is penetrated by a plurality of apertures in which the electrodes are positioned to extend through a lower chamber lying between those two supporting plates. Commonly, each electrode includes a fuse that extends upwardly from the electrode to an electrical contact plate through an upper chamber lying between the electrode support plate and the contact plate. Air is drawn into the upper chamber, into the interior of the electrodes, down the electrodes to their open bottoms, into the space between the electrode and dielectric tubes, up through the corona discharge field to produce ozone, and out the open upper end of the dielectric tubes into the lower chamber, from which the mixed air and ozone is withdrawn for use.
Corona discharge ozone generators of the prior art are effective at producing ozone, and are fairly reliable. However, the ozone generating process is a high energy process, and the high energy corona discharge field maintained within each ozone generating cell can have destructive effects on the generating cell components, requiring generating cell maintenance and occasional replacement. In an ozone generator of the prior art, any maintenance activity that requires access to one or more of the dielectric tubes requires an almost complete disassembly of the generator. An upper closure plate must first be removed, then the electrical contact plate, and then the electrode support plate and all electrodes supported from it, before the upper ends of the dielectric tubes are exposed. During the procedure of removing the electrode support plate and electrodes, and the reverse process of reinstalling them, the risk of damage to electrodes and dielectric tubes is high.
Operational failure of one or more ozone generating cells within an ozone generator of the prior art can also present significant problems in addition to the difficult and time consuming procedure necessary to gain full access to the cells. In the event of a cell failure arising from a dielectric tube fracture, cooling water will immediately enter the tube, electrically short the electrode to ground, and cause the fuse connecting the electrode to the high voltage source to fail. A more significant problem associated with a tube fracture, however, is the potential for flooding of the lower chamber to which all dielectric tubes of the generator open. Water entering that chamber will flood into all dielectric tubes and bring about a catastrophic, cascading failure of all generating cells.
A similar problem can result in the event of a back flow of water from downstream in the treatment system of which the generator is a part. In a back flow situation, water will back up in the conduit carrying ozone to distribution, and into the lower chamber of the ozone generator, to which all dielectric tubes open. Water that enters that chamber will flow into all of the dielectric tubes and precipitate a complete failure of the entire ozone generator system by shorting all of the electrodes.
The problems and increased risk of failure associated with ozone generating systems of the prior art have not been effectively addressed, and contribute to reluctance to utilize ozone in water treatment operations, especially in circumstances in which generator failures can cause extended down time in the functioning of the treatment facility. There remains a need for an ozone generator system that avoids the disadvantages of the prior art and provides a much more reliable source of ozone.